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how to avoid the complex result when using ifft2

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Donyau Chiang
Donyau Chiang 2016-6-24
关闭： MATLAB Answer Bot 2021-8-20
How are you? I tried to solve an optical intensity distribution problem, based on the theory derived from Prof. J.W. Goodman and Prof. M. Mansuripur. My code is below: % calculate the intensity pattern for the x- and z- polarized light at a distance % of z=20 from a aperture of radius r0=3, the original polarized being x
close all; clear all;
r0=3.; nod=256; L=10*r0; z0=20.; det=L/nod; du=1/L;
xyp=(-nod/2:nod/2-1)*det; [xp,yp]=meshgrid(xyp,xyp);
% create a circle of radius r0=3 vn1=find(sqrt(xp.*xp+yp.*yp) <= r0); t1=zeros(nod,nod); t1(vn1)=ones(size(vn1));
uv=(-nod/2:nod/2-1)*du; [u,v]=meshgrid(uv,uv); vn2=find(sqrt(u.*u+v.*v) <= 1); A1=zeros(nod,nod); A1(vn2)=ones(size(vn2));
% do the FFT for circle aperture T1=fftshift(fft2(t1)); T1=T1.*A1;
sgz=sqrt(ones(nod)-u.*u-v.*v);
% create x-polarized component fxx fxx=(ones(nod)+sgz-u.*u)./((ones(nod)+sgz).*sqrt(sgz)); gt=exp(i*2*pi*z0*sgz); ta=((T1.*fxx).*gt); tb=ifft2(ta); Ta=tb.*conj(tb);
mesh(xp,yp,Ta)
% create z-polarized component fxz fxz=-u./sqrt(sgz); tc=((T1.*fxz).*gt); tc=ifft2(tc); Tb=tc.*conj(tc);
figure mesh(xp,yp,Tb)
I get the error message from MatLab as: Error using ==> surface X, Y, Z, and C cannot be complex.
But if I use L=100*r0, I can get the result. Could someone teach me the restriction to use ifft2 command? Your help will be great appreciated. With best Regard Donyau

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